Plainfield is a city in Union County, in the U.S. state of New Jersey. Nicknamed "The Queen City", it serves as both a regional hub for Central New Jersey and a bedroom suburb of the New York Metropolitan area, located in the Raritan Valley region. As of the 2020 United States census, the city's population, majority Latino for the first time, was 54,586. This was an increase of 4,778 (+9.6%) from the 2010 census count of 49,808, which in turn reflected an increase of 1,979 (+4.1%) from the 47,829 counted in the 2000 census. In 2022, the Census Bureau estimated the city's population to be 54,513.

Union County is a county in the northern part of the U.S. state of New Jersey. As of the 2020 United States census, the county was the state's seventh-most-populous county with a population of 575,345, its highest decennial count ever and an increase of 38,846 (+7.2%) from the 2010 census count of 536,499. Its county seat is Elizabeth, which is also the most populous municipality in the county, with a 2020 census population of 137,298, and the largest by area, covering 13.46 square miles (34.9 km2). The county serves as a transition point between the Central Jersey and North Jersey regions of the state.